1. Field of the Invention
The present invention relates to an adhesive-applied tape, and particularly it relates to an adhesive-applied tape consisting of a support film provided with an adhesive layer containing a mixture of an amorphous polyimidosiloxane and an epoxy resin, as well as to an adhesive-applied tape which is further covered with a releasable protective film having surface tackiness.
The adhesive-applied tape of the present invention requires no high-temperature contact bonding and thus has high electrical reliability, while the adhesive layer is flexible to thus minimize warpage resulting from the adhesive layer, and it may therefore be suitably used for electronic parts which require heat resistance.
2. Description of the Related Art
Laminated boards, including flexible circuit boards, have conventionally been produced using adhesives of epoxy resins or the like to adhere substrates of polyimide films or the like to metal layers, and although the polyimide films themselves have excellent heat resistance there exists a problem in the poor reliability of the epoxy resin adhesives.
Polyimide films are often directly attached to copper foil conductors, but since conventionally used polyimide films are in the form of polyimide-based precursors when applied onto metal foils they require heat treatment at 350-450.degree. C., which causes heat deterioration of the copper foils.
Processes are also known which do not use epoxy resins but involve direct casting of polyimide dope solutions onto the copper foils followed by heat treatment; however, since heated contact bonding at high temperature is necessary for increased productivity, problems such as deterioration and warping of the copper foils have resulted.
On the other hand, TAB tapes which conventionally employ adhesives such as B-stage epoxy resins on polyimide films are associated with a number of problems, including warping, problems with migration characteristics, difficulties with fine pitch matching, problems in terms of pot-life (storage stability), required prebaking for long periods of about 10 hours at 50.degree. C. for attachment to copper foils after punching, and squeeze-out or exudation of the adhesive layer.
For these reasons, although many different polyimide-based adhesives have been proposed, they still have problems in that warping occurs when they have excellent heat resistance, or else they have insufficient adhesive strength and inferior heat resistance.
Furthermore, known adhesives which are formed into tapes have been found to have such problems as reduced adhesive strength of the laminates which employ such adhesive tapes, due to adhesion of dirt onto the adhesive.
In other words, with the use of conventional adhesives and adhesive-applied tapes (or films) it has not been possible to obtain adhesive-applied tapes which do not require high-temperature and high-pressure contact bonding conditions for contact bonding, which undergo substantially no warping of the laminate as a result of the adhesive under high-temperature heating, which have excellent migration characteristics of the adhesive layer, which have no exudation of the adhesive, have satisfactory storage stability and undergo minimal squeeze-out when pasted to metal foils.